The present invention relates to a test device and determination of a chemical or biochemical component (analyte) in an aqueous body fluid, such as whole blood or interstitial fluid. In particular the present invention relates to a dry reagent test device from which an analyte presence and/or concentration is determined by use of an instrument and a disposable capillary reagent carrier and acquisition device. A common use of such test devices is for determination of glucose level in blood by diabetics.
Numerous devices have been developed to test for presence and quantity of analytes in aqueous samples, such as whole blood or urine. The patent and technical literature of the last years is replete with inventions which utilize a reagent strip containing a dry chemistry reagent system, that is, a system in which the wet chemistries are imbibed into an absorbent or bibulous medium, dried, and later reconstituted by fluid from the test sample. The reagent strips contain an indicator which changes color, depending on the presence or concentration of a particular analyte in a biological fluid applied to the strip. These strips may be read visually by reference to a color standard or colorimetrically by instrument calibrated or programmed to detect a certain color. Although some of these strips use reduction chemistries, more commonly they involve an oxidizable dye or dye couple. Some of the strips include an enzyme, such as glucose oxidase, which is capable of oxidizing glucose to gluconic acid and hydrogen peroxide. They also contain an oxidizable dye and a substance having peroxidative activity, which is capable of selectively catalyzing oxidation of the oxidizable dye in the presence of hydrogen peroxide. (See, for example, U.S. Pat. No. 4,935,346, to Phillips et al.) Examples of these devices, in addition to those used to test blood glucose, include tests for cholesterol, triglycerides, calcium or albumin in whole blood, and for protein, ketones, albumin or glucose in urine.
Dry chemist reagent strips incorporating enzyme-based compositions are used daily by millions of diabetics to determine blood glucose concentrations. The NIH sponsored study, the Diabetes Complications and Control Trial, demonstrated conclusively that careful control of blood glucose levels can significantly reduce the incidence of serious complications of diabetes such as vision loss and kidney malfunction. Most diabetics must test themselves periodically in order to make appropriate adjustments to their diet or medication. It is thus especially important for diabetics to have rapid, inexpensive, and accurate reagent strips for glucose determination. The embodiment of dry chemistry reagent systems in test strips enable simple yet effective analytical protocols.
The technologies embodied in the products which have been developed to date have certain limitations from the perspective of the end user and/or the manufacturer. There is, therefore, a need to overcome some of the limitations of currently available testing systems. U.S. Pat. No. 3,092,465, issued to Adams et al., U.S. Pat. No. 3,298,789, issued to Mast and U.S. Pat. No. 3,630,957, issued to Rey et al., all describe a basic reagent system which became a standard for colorimetric determination of glucose in biological samples. These patents describe the formation of a film layer or semi-permeable coating over the bibulous matrix to hold back the larger particulates, such as red blood cells, and allow fluid to permeate into the bibulous matrix. This approach requires the removal of red blood cells by washing or wiping to enable visual inspection or instrument reading of the indication of the dye color formed in the matrix.
Stone, U.S. Pat. No. 3,607,093, discloses a membrane for testing blood where the membrane has a skin permeable to solutions but impermeable to solids such as red blood cells and to macromolecules such as proteins. This membrane is disclosed as being used by applying a blood sample then wiping away the red blood cells from the skin in order to reach the test indication through the skin.
U.S. Pat. 3,552,928, issued to Fetter discloses the use of certain water soluble salts and amino acids in reagent formulations as separation agents to provide blood separation. With solids such as red blood cells substantially removed from the biological fluid, there is less background color at the test site to obscure a change in coloration produced by a testing reagent.
Phillips et al., U.S. Pat. No. 4,935,346 discloses a system wherein a whole blood sample is applied to the device and indicator development occurs in the presence of the colored components of the sample. Measurements of the color change in indicator are made at two distinct wavelengths to eliminate the interferences from the presence of colored blood components.
Terminello et al., U.S. Pat. No. 4,774,192, disclose a system in which the matrix is formed of an asymmetric material used to filter the red blood cells in the sample. The asymmetric material has a density gradient from one side to the other to progressively separate red blood cells from the fluids.
Erikson, et al., U.S. Pat. No. 5,582,184 disclose a system which uses a small capillary tube, membrane, and infrared testing.
Daffern et al., U.S. Pat. No. 4,994,238, disclose a test device that comprises an asymmetric reagent layer that has progressively finer filtration with increased distance from one surface toward the other surface.
Castino et al., U.S. Patent No. 5,456,835 disclose the use of filters formed of ligand modified polymeric film such as polypropylene fibers and polyethersulfone fibers.
Vogel et. al., U.S. Pat. No. 4,477,575, disclose the use of glass fiber material to achieve blood separation through the thickness of the material. Blood is applied to one side of the glass fiber, and relatively clear fluid migrates out of the opposite side. This fluid is delivered to an additional layer where the detection of analytes can occur.
Macho et al., U.S. Pat. No. 5,451,350, disclose the use of absorbent channels to distribute sample fluid in multi-zone test devices. Charlton et al., U.S. Pat. No. 5,208,163, also disclose the use of capillary channels to distribute blood to various chambers in the device.
Pending U.S. patent application Ser. No. 08/628,489 (published as PCT International Publication No. WO 97/38126) describes the use of microporus material and the concept of microtitration which are well suited for this application.
Ash et al., U.S. Pat. Nos. 4,854,322 and 4,77,953 disclose a capillary filtration and collection device for long term monitoring of blood constituents which is implanted within the interstitial body space in fluid communication with blood capillaries.
The disclosures of the above patents are incorporated herein by reference.
The prior art devices and methods of the above references provide varying degrees of effectiveness of blood analysis at varying degrees of complexity and cost.
It is an object of the present invention to provide improved devices and methods to improve the performance and minimize the cost and complexity compared to the prior art devices.
It is a further object of the present invention to provide a fully disposable, discrete reading system for detecting an analytes presence or concentration.
It is another object of this invention to provide capillary format for testing which provides an easy to use, low volume device which is easy to manufacture.
It is another object of this invention to provide capillary format for testing which permits the patient to use non traditional body locations to extract a sample of body fluids.
It is another object of this invention to provide a means for measuring low volume body fluids such as interstitial fluid.
It is still a further object of this invention to provide a dry chemistry reagent and test strip which can be used in an electronic meter to analyze body fluids for one or more analytes.
The above objects as well as others are achieved by the devices, methods and systems of this invention as disclosed herein.
In one aspect this invention provides a method of testing or analyzing body fluids for the presence or concentration of an analyte by using a porous matrix. The porous matrix is provide through the use of hollow fiber made from various polymers including polyethersulphone, polysulphone, polyurethane, and other hydrophilic polymers. The hollow fibers can be dual skin in that they have two skins; one on the inner diameter and one on the outer diameter with various pore structures connecting the two skins, or have a single inner diameter skin with an isotropic pore structure radiating outward. The pore size of these skins can be either similar or dissimilar, but preferably should not be less than 0.1 microns and less that 5 microns in size.
In a preferred embodiment of the invention the device comprises of a capillary system which is used to collect the sample of body fluid. The capillary is the hollow portion of the hollow fiber. The sample is wicked up the hollow fiber and wets out the fiber matrix which is used as the membrane for analysis. The use of a hollow fiber capillary tube to collect the sample permits the patient the ability to collect a very small sample from any body location thereby increasing the number of possible sampling sites and body fluids where the patient can extract a sample of body fluid. The apparatus comprises of a hydrophilic hollow fiber capillary. The matrix can then be tested using various techniques including infrared, electrochemical, or colormetric means. When using the matrix which forms the hollow fiber matrix for electrochemical or colormetric analysis, it is imbibed with indicator capable of indicating the presence or concentration of the analyte. The hollow fiber capillary can be cast from a hydrophilic compound, or hydrophilic agents can be coated either prior to or during reagent application.
The test method comprises applying a blood sample to the hollow fiber capillary by placing the hollow fiber capillary tube in communication with the sample and, allowing it to wick up the tube and wet out the matrix of the hollow fiber. This permits the fluid to pass through the hollow fiber capillary spreading onto the matrix. The reading or measuring for the presence/concentration of the analyte being tested is accomplished by detecting the change in reflectance of the indicator reagent for a colormetric test which is imbibed into the matrix.
The embodiments of the devices of the invention with the appropriate dry chemistry system in the matrix member can be used in test strips which may be read or measured in an electronic meter.
The above sets forth the generic aspects of the device and methods of the present invention. These device and methods are more fully described in the drawings and the descriptions below.